This invention relates to a radiation detector used in high energy physics or diagnostic radiology such as an X-ray computerized tomographic apparatus (X-ray CT) and a positron emission nuclide tomographic apparatus (positron CT).
A radiation detector having a photomultiplier tube and a scintillator WHICH generates scintillated light from irradiated radiation and then the photons of the light are detected by the photomultiplier tube. The scintillator thus is required to meet the following conditions:
(1) the scintillator should transmit to the photomultiplier tube the maximum of the fluorescence which it generates, and
(2) reflecting layers applied to the scintillator should be high in reflectance, stable and exempt from any alteration and discoloration, all over the entire ultraviolet to visible light range. Several types of scintillators satisfying these requirements have so far been commercialized.
One example of such a commercial use is disclosed in Japanese Patent Provisional Publication No. 57-194374. The conventional radiation detector thus disclosed uses, as the Bi.sub.4 Ge.sub.3 O.sub.12 crystal (referred to as "BGO crystal"), having reflecting layers of BaSO.sub.4 with a binder consisting of polyvinyl alcohol (referred to as "PVA binder").
When forming conventional reflecting layers for a BGO crystal from BaSO.sub.4 with PVA binder, the reflectance of the reflecting layers is likely to fluctuate and the reflecting layers frequently exfoliate from the BGO crystal. These disadvantages are caused by permeation of silicone based adhesive material commonly used to adhere the BGO crystal to the photomultiplier tube into the reflecting layers. This permeation reduces the reflectance of the layers and adhesion.
There is another disadvantage in the manufacturing process of conventional reflecting layers. The reflecting layers are made into multiple layers from aqueous solutions of different concentration of PVA mingled with BaSO.sub.4 and the respective coating steps makes the process onerous and expensive.